118. Pascal's Triangle

118. Pascal’s Triangle

Given a non-negative integer numRows, generate the first numRows of Pascal's triangle.


In Pascal's triangle, each number is the sum of the two numbers directly above it.

Example:

Input: 5
Output:
[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

public List<List<Integer>> generate(int numRows) {
    List<List<Integer>> result = new ArrayList<>();
    if(numRows == 0) return result;
    result.add(Arrays.asList(1));
    for(int i = 1; i < numRows; i++) {
        ArrayList<Integer> temp = new ArrayList<>();
        List<Integer> lastRow = result.get(i-1);
        temp.add(1);
        for(int j = 1; j < lastRow.size(); j++) {
            temp.add(lastRow.get(j-1) + lastRow.get(j));
        }
        temp.add(1);
        result.add(temp);
    }
    return result;
}